That stated, this woman is deaf, her dog probably actually does perform some service.
And why complain about allergies and size at the END of the trip? Wouldnt that come up early?
The service animal is supposed to do things like prevent the master from crossing a street when traffic is coming. A chihuahua can't physically exert enough force to stop a large adult from going into harm's way. I have a cousin who trains service animals for veterans but is also blind and trains her own seeing eye dogs. She's about 5'10" and prefers to have large German Sheppards as her seeing eye dogs.
I wasnt saying to use lap dogs, just limit the size.
German ShepHERDs (sorry, the spelling drives me nuts...its a sheep-HERDing dog) are ideal, of course. (Highly biased here, but with good reason.)